An inverter control apparatus for driving a motor mounted in a compressor or a blower used in a refrigerating or an air-conditioning system generally has the following structure: AC power fed into a refrigerating system undergoes full-wave rectification in a rectifier circuit, and passes across a smoothing capacitor having a great enough capacitance and being hooked up between output terminals. This structure allows driving an inverter with a DC power supply having a small ripple content, and also absorbing regenerative energy which is produced when the motor stops or slows down, so that an over-voltage can be prevented.
In recent years, smoothing capacitors have been targeted to substantially reduce their capacitance in order to downsize the motor drive inverter control apparatuses. The related art is disclosed in, e.g. Japanese Patent Unexamined Publication No. 2002-51589. The conventional motor drive inverter control apparatus is described hereinafter with reference to the drawings. FIG. 6 shows a block diagram illustrating a motor drive inverter control apparatus that employs a conventional capacitor having small capacitance.
As shown in FIG. 6, the conventional motor drive inverter control apparatus has the following mechanism: The power fed by AC power supply 1 is received by rectifier circuit 2, of which output is coupled to smoothing capacitor 3, and capacitor 3 has a small enough capacity as smaller as 1/100 those of conventional ones.
Inverter 4 is formed of 6 pieces of switching elements (including reversed diodes) coupled together into a three-phase bridge, and coupled in parallel to smoothing capacitor 4. Motor 5 generally employs a brush-less motor, and three-phase windings are provided to its stator. Respective ends of the three-phase windings are coupled to an output of inverter 4.
Control circuit 7 is hooked up to the inverter control apparatus such that it receives information including voltage “v” of AC power supply 1, current “idv” of a DC section, output current “ia”, “ib” and “ic” of inverter 4, and rotational position θ of motor 5 obtained by position detecting means 6. Control circuit 7 controls the gates of inverter 4 by inputting the information thus obtained such that the motor can be driven optimally.
If control circuit 7 damps the operation of motor 5, regenerative energy flows into the power supply via the diodes inversely hardwired. At that time, since smoothing capacitor 3 has a small enough capacity, it cannot fully absorb the regenerative energy. As a result, the power supply voltage rapidly rises, and an over-voltage sometimes degrades respective driving elements.